The role of metal hydroxide complexes in late transition metal-mediated transmetalation reaction: The case of gold

Article abstract of DOI:10.1002/adsc.201200233

In gold chemistry, the hydroxide function on the metal center was observed to act as a potent transmetalation group facilitator when reacted with boronic acids leading to the exceedingly rapid formation of gold-aryl bonds. Copyright

Full text of DOI:10.1002/adsc.201200233

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DOI: 10.1002/adsc.201200233
The Role of Metal Hydroxide Complexes in Late Transition
Metal-Mediated Transmetalation Reaction: The Case of Gold
Stꢀphanie Dupuy,a Luke Crawford,a Michael Bꢁhl,a Alexandra M. Z. Slawin,a
and Steven P. Nolana,*
a
EaStCHEM School of Chemistry, University of St Andrews, St Andrews, KY16 9ST, U.K.
Fax : (+44)-(0)1334-463-808; e-mail: snolan@st-andrews.ac.uk
Received: March 24, 2012; Revised: June 23, 2012; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201200233.
Abstract: In gold chemistry, the hydroxide function
on the metal center was observed to act as a potent
transmetalation group facilitator when reacted with
boronic acids leading to the exceedingly rapid for-
mation of gold-aryl bonds.
bution was made by Gray and co-workers in 2006
when they reported an efficient and selective proce-
dure using a variety of (hetero)arylboronic acids in
the presence of Cs2CO3 to access, in good to high
yields, phosphane-gold(I) aryls (Scheme 2).[6] Further
studies demonstrated that this methodology was also
successful using a Cl precursor[7] and either sterically
demanding dialkylbiarylphosphine and N-heterocyclic
carbene ligands (NHC) or bulky coupling partners.[8]
Subsequent investigation led the same group to dem-
onstrate further utilities of boronic acids and esters to
provide in good yields diaurated compounds.[9] This
fundamental reaction is of further interest as the
Keywords: arylboronic acids; gold hydroxide com-
plexes; gold-aryl complexes; N-heterocyclic car-
benes; transmetalation
Over the past ten years, the use of gold in homoge- transmetalation reaction represents a key step in the
nous and heterogeneous chemistry has witnessed an possible role of gold in cross-coupling reactions.
explosive growth.[1] A key step in catalyst regenera-
Inspired by those first reports, we envisaged initial-
tion in these catalytic reactions is the protodeauration ly to expand the scope of the reaction using (NHC)-
of an organogold intermediate. To obtain insight into gold(I) complexes,[10] with the aim of developing
this mechanism, trapping of such an intermediate has a novel, robust methodology of broad synthetic utility
recently been the goal of a number of research and generality for the preparation of substituted
groups.[2] Common straightforward routes to access (NHC)-gold(I) aryl complexes. As far as we are
these involve the reaction of lithium or Grignard re- aware, no mechanistic studies have been performed
agents with a [Au(I)(L)(Cl)] (L is 2-electron donor) for such gold reactions until now. Therefore, to probe
complexes (Scheme 1).[3] However, these procedures the inner workings of this fundamental reaction step
suffer from a narrow range of functional group toler- using gold, experiments and calculations probing the
ance and poor conversion when sterically hindered mechanism were next envisioned.
substrates are employed.
An initial experiment was conducted using [Au-
ACHTUNGTREN(NUGN IPr)Cl] (IPr=1,3-bis(diisopropyl)phenylimidazol-2-
To address these limitations, recent investigations
have focused on using organoboron-based reagents ylidene) 1 (a Cl not Br bearing precursor) and
known for their air stability and high tolerance of sen-
sitive functionality. The seminal work of Schmidbaur[4]
and Fackler[5] has highlighted the transfer of a phenyl
group from a sodium tetraphenylborate to gold(I)
proceeding at room temperature. A significant contri-
Scheme 1. Common routes to access organogold(I) com-
plexes.
Scheme 2. Transmetalation of arylboronic acids to phos-
phane-gold(I) complexes using Grayꢂs conditions.
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Table 1. Optimization of the transmetalation of boronic acids to (NHC)-gold(I) complexes.
Entry
Solvent
Base
Time [h]
Temperature [8C]
Conversion [%][a]
1
2
3
4
5
6
i-PrOH
i-PrOH
THF
benzene
toluene
toluene
toluene
toluene
toluene
CsCO3
KOH
KOH
KOH
KOH
KOH
KOH
KOH
24
24
24
24
24
1
1
1
24
70
70
70
70
70
50
r.t.
r.t.
r.t.
100
100
100
100
100
100
100
100
0
7
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
8[b]
9
[a]
1
Determined by H NMR spectroscopy (isolated yields are given in brackets).
Using 1 equiv. of phenylboronic acid.
[b]
2 equivalents of phenylboronic acid 2 as substrate
Further optimizations were carried out in toluene
under the conditions previously described by Gray.[6] as reaction solvent as its use made the reaction com-
After 24 h, the reaction reached completion. The re- pletion easy to monitor with all organometallic spe-
action conditions were next optimized and results of cies becoming soluble at the endpoint. As expected,
this optimization are summarized in Table 1. We were no reaction occurred in the absence of base.
pleased to see that the reaction proceeded smoothly
With this new protocol in hand, the substrate scope
when replacing Cs2CO3 with less expensive KOH and limitations of the reaction were explored. The re-
base (Table 1, entry 2). Further optimization showed sults are summarized in Table 2. Phenylboronic acids
that a complete conversion could be obtained at am- with both electron-donating and electron-withdrawing
bient temperature (Table 1, entry 7). Also, the reac- substituents afforded the corresponding organogold
tion time could be shortened from 24 h to 1 h. Grati- complexes in good to excellent yields within 10 h. In
fyingly, one equivalent of boronic acid was sufficient most reactions, one equivalent of boronic acid was
to lead the reaction to completion (Table 1, entry 8).
sufficient for the reaction to reach completion in the
Table 2. Transmetalation of arylboronic acids to [AuACTHNUTRGNE(UNG IPr)Cl] (1).
Entry
1
Boronic acid
Time [h]
1
Product
Yield [%][a]
>99
2[b]
2
6
>99
3
84
4
7
97
2
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The Role of Metal Hydroxide Complexes in Late Transition Metal-Mediated Transmetalation Reaction
Table 2. (Continued)
Entry
Boronic acid
Time [h]
1
Product
Yield [%][a]
5
>99
6
7
2
66
0.3
>99
8[b,c]
1.5
10
2
77
9
>99
78
10[c]
11
4
90
12
0.25
91
13
1
2
3
86
92
88
14
15[c]
16[c]
17[c]
10
88
5
62
0
18
24
[a]
Isolated yields.
508C.
Using 2.5 equiv. of boronic acid
[b]
[c]
reported time. We were pleased to see that the pro- fording the corresponding 2-biphenylgold(I) in 97%
cess was not sensitive at all to halogenated substrates yield (Table 2, entry 4). For direct comparison, under
while these substrates would have suffered from com- heating using bulky (dicyclohexyl)(2-biphenyl)phos-
peting side-reaction using organolithium or Grignard phine ligand the reaction required 30 h to reach com-
reagents (Table 2, entries 5, 6, 7 and 11). The reaction pletion and the corresponding biphenylgold was ob-
proceeded smoothly with o-biphenyl substituent af- tained in 90% yield.[8c] Rapid reactivity (<30 min)
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was encountered in the case of 3,4-dichlorobenzene- Ccarbene bond distances are identical within experimen-
boronic acid (Table 2, entry 7) and 4-[(tert-butyldime- tal error in 5 and 17 and are similar to those previous-
thylsilyl)oxy]phenylboronic acid (Table 2, entry 12). ly encountered for gold-NHC complexes (ranging
These led to quantitative yields of the expected prod- from 1.942 to 2.018 ꢄ).[6,8c,12] The Au Caryl bond
À
ucts.
lengths are also equal in both complexes and compa-
À
Slightly longer reaction times were required for 4- rable to previously reported Au C bonds in NHC
methoxyphenyl substituent (Table 2, entry 9). No complexes.[6,8c,12] The aryl group bound to the gold
clear influence of the electronic environment could be center in the two crystal structures is almost perpen-
observed but as previously reported the use of bulkier dicular to the imidazole core in order to minimize any
substrates such as mesitylene or xylene required an steric hindrance between the ortho-substituent groups
increase to 2.5 equivalents of the starting material and the isopropyl groups of the NHC ligands.
(Table 2, entries 15 and 16). Still the arylgolds were
Although known since the first report of carbon-
obtained in good yields (88% yield). Direct compari- carbon coupling by Suzuki and extensively studied,
son with phosphane systems developed by Gray only the mechanism of transmetalation has long remained
allowed, for example, isolation of the corresponding obscure. The role of the base was especially unclear.
phosphane mesitylgold(I) in 87% yield after 60 h.[8c] Plausible hypotheses involve it in either the formation
Similar to Grayꢂs work, an increase to 2.5 equivalents of an “ate” complex at the boron or to coordinate the
for the 4-nitrophenyl- and ferrocenylboronic acids metal to form a metal hydroxo complex.[13] Very re-
was needed to drive the reaction to completion cently, Hartwig[14] and Amatore and Jutand[15] have re-
(Table 2, entries 8 and 17).[6] The tendency of sulfur to ported kinetic studies of stoichiometric reactions ex-
form strong bonds to gold could explain the lack of ploring the two possible pathways. Their results sup-
reactivity for 2-thiopheneboronic acid. Overall, vari- port a hypothesis where the transmetalation reaction
ous functionalities are tolerated by this methodology involves a palladium hydroxide reacting with the bor-
including methoxy, amino, bromide, chloride, nitro onic acid. Thus we hypothesized two plausible path-
and fluoride, which can permit further synthetic deri- ways for our gold transmetalation reaction
vatization or functionalization. This NHC system (Scheme 3).[16] Path A involves the initial coordination
shows closely related reactivity as the phosphane- of the hydroxide to the boron to form phenylborate
based system developed by Gray. Representative species 20 (Scheme 3, Path A).
crystal structures of two organogold compounds, ob-
This would enhance the nucleophilicity of the or-
tained by slow diffusion of pentane into a saturated ganic group on boron and thus facilitate its transfer to
dichloromethane solution containing the complex, are the more electropositive gold center. The second
shown in Figure 1.[11]
pathway (Scheme 3, Path B) would first involve the in
Complexes 5 and 17 exist as two-coordinated, situ formation of [Au
(IPr)(OH)] (21)[17] that would
gold(I) complexes, as expected. In 17, a nearly linear react with the organoboron species to afford the final
AHCTUNGTRENNUNG
À
À
environment for the Ccarbene Au Caryl bond angle is arylgold. Experiments were carried out to determine
present, very close to 1808, as expected for NHC- which of the two possible pathways was involved in
À
À
gold(I) complexes while in 5 the Ccarbene Au Caryl this reaction manifold. To probe the viability of both
bond angle is slightly distorted. Moreover, both Au
pathways, “intermediates” 20 and 21[17] were respec-
tively reacted with 1 and 2. The progress of the reac-
tions was monitored by NMR spectroscopy [Eq. (1)
and Eq. (2)].
À
Phenyltrihydroxoborate 20 reacted with 1 in a 1:1
ratio in toluene-d8 at room temperature and afforded
3 in 1 h [Eq. (1)]. Similarly, the gold hydroxide 21 was
Figure 1. Ball-and-stick representations of [Au
5 (left) and [Au(IPr)(C9H11)] 17 (right). Hydrogen atoms
have been omitted for clarity. Selected bond distances (ꢄ)
ACHTUTGNRENNUG(IPr)ACHUTNGTRNE(NUGN C12H9)]
A
ACHTUNGTRENNUNG
À
À
and angles (deg) for 5: C31 Au1 2.052(17), Au1 C1
À
À
À
2.026(10), C1 Au1 C31 172.5(6). For 17: Au1 C4 2.050 (5),
Scheme 3. Two plausible pathways for the transmetalation
reaction involving gold.
À
À
À
Au1 C2 2.023(5), C2 Au1 C4 178.1(2).
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The Role of Metal Hydroxide Complexes in Late Transition Metal-Mediated Transmetalation Reaction
Scheme 4. Possible reaction pathway leading to [AuACHTNUTRGENN(UG IPr)ACHTUNGTRENN(GUN C6H5)] (3).
reacted with phenylboronic acid 2 in a 1:1 ratio at
With this first insight of the nature of the active
room temperature [Eq. (2)]. The latter reaction species in the reaction, it could therefore be also en-
proved instantaneous! Such a significant difference in visaged that a similar pathway could occur using
reactivity clearly illustrates that pathway B is more Grayꢂs conditions, especially using a protic solvent
facile and suggests that, as with palladium in the such as 2-propanol in the presence of cesium carbon-
Suzuki–Miyaura reaction, transmetalation of boronic ate as base (Scheme 5). The formation of a gold iso-
acids to gold may very well proceed through the for- propoxide intermediate iiia may occur and be hy-
mation of a metal hydroxide complex (Scheme 4).
These experiments point out that pathway B will be cies iiib could be formed if traces of water were pres-
the favored one if the in situ [Au(IPr)(OH)] can be ent in the medium. The latter would then react with
pothesized as an active species. Or a hydroxide spe-
AHCTUNGTRENNUNG
formed during the reaction. This would obviously either arylboronic acid or activated arylborate to
depend of the reaction conditions and on the nature afford the desired arylgold compound.
of the base used. Thus under our reaction conditions,
The transmetalation reaction was modelled using
the presence of both the trihydroxoborate and gold DFT calculations.[18] Calculations were performed on
hydroxo species cannot be excluded and both path- the reaction between phenylboronic acid 2 and 21 and
ways may be involved. Indeed, the transmetalation of results confirm that no significant activation barrier
20 to 21 was experimentally determined to also be exist when the reaction proceeds through Path B
possible [Eq. (3)].
(Figure 2). Several transition states were also located
and have similar energies to the starting material. The
proposed first transition state contains a “boronate
complex” formed via coordination of the O atom of
21 and the boron atom of the boronic acid. The
second transition state corresponds to the formation
of a cationic gold complex facing the phenyl group of
This result is not without reminding us of the semi- the boron species in order to preserve the “hypercoor-
nal work of Schmidbaur in which a gold oxide [(t- dination” of the boron center.
Bu)3PAuO]BF4 was successfully reacted with
With our computational protocol the entry into
path B, that is, formation of 21 from 1, is more diffi-
NaBPh4.[4]
Scheme 5. Plausible pathways using Grayꢂs system
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be isolated. But when 21 was used as a gold source,
both reactions proceeded to completion within 30 min
[Eq. (5)] and both products 24 and 25 could be isolat-
ed in good yields. As expected, the less activated 2-
formylbenzeneboronic acid reacted more slowly than
its para-substituted relative.
In summary, we have described the development of
a new methodology for the transmetalation from bor-
onic acids to NHC-gold(I) complexes. Mild conditions
were used as compared to previous reports for this re-
action and our process is as efficient as other recently
reported gold systems, even better for some sub-
strates. This method is a practical alternative to the
Figure 2. Energy profile for the transmetalation Path B
(PBE0-D3 level), see Supporting Information, Figure S1 for
an enlarged colour version.
cult to model quantitatively, because of the large use of lithium or Grignard reagents for the synthesis
medium effects on the small ions OHÀ and ClÀ and of variously functionalized organogold compounds.
the possible need to include counterions as well. Moreover, mechanistic studies enabled us to obtain
From the conditions necessary for this reaction, how- a clearer picture of the active species in this reaction
ACHTUNGTRENNUNG
ever,[7b] it is clear that substantial activation is needed. and may be extrapolated to other previously devel-
Likewise path A is difficult to model because one oped gold systems. These studies have shown that the
of the putative products, B(OH)3ClÀ, is inherently un- reaction occurs preferentially through the “hydroxide
stable in the gas phase. We were able, however, to pathway” rather than the expected “borate pathway”.
locate a transition state for substitution of the chlo- Although pathway B is the kinetically favored reac-
ride ligand in 1 with the boronate 20, affording an al- tion route, pathway A cannot be excluded under the
ternative entry into path B (see Figure S2 in the Sup- experimental reaction conditions. The present results
porting Information,). A low enthalpic barrier for this provide the first key fundamental insight into the
“in-situ” formation of the hydroxide is computed, ca. mechanism of transfer of the organic fragment from
7 kcalmolÀ1, but because the interaction between the boron to gold and establishes that the reactivity of
reactants is weak, the entropic penalty for this asso- gold is similar to that of palladium for this important
ciative process imparts some kinetic hindrance. In fundamental reaction step. Furthermore, the fact that
contrast, complex formation between 2 and 21 (to gold mimics palladium along this reactivity manifold
form INT1 in Figure 2) is quite exothermic, which suggests to us that other late transition metal hydrox-
should be an important factor contributing to the en- ides (or more generally LTM alkoxides[20]) may
hanced reactivity of 21 compared to that of 1.[19]
With evidence of [Au(IPr)(OH)] 21 being an active this transmetalation reaction of boron to gold could
behave in this manner. The basic understanding of
AHCTUNGTRENNUNG
species, it was reacted with several boronic acids em- also allow for further synthetic functionalization (or
ploying our previously optimized protocol. All reac- to rapidly gain molecular complexity) in one-pot reac-
tions involving 21 reached completion within 5 min tions involving diverse electrophiles. The reactivity of
[Eq. (4)].
these organogold complexes is the subject of ongoing
studies in our laboratories.
Experimental Section
General Procedure for the Synthesis of Arylgold
Complexes
When the initial scope of the reaction was explored,
the 2- and 4-formylbenzeneboronic acids did not lead
to product under our conditions. One hypothesis was
simply that a side-reaction such as the Cannizzaro re-
A scintillation vial was charged with [AuACTHNUTRGNE(NUG IPr)Cl] (1) (50 mg,
0.08 mmol), KOH (9 mg, 0.16 mmol) and the corresponding
arylboronic acid (0.08 mmol) in toluene (0.8 mL). The reac-
action had occurred, although no side-products could tion mixture was stirred at room temperature and monitored
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The Role of Metal Hydroxide Complexes in Late Transition Metal-Mediated Transmetalation Reaction
1
by H NMR spectroscopy. Upon completion, the solvent was
removed under vacuum, the residue extracted into benzene,
and filtered through Celite. The filtrate was taken to near
dryness and pentane was added to precipitate the product.
The resulting white suspension was filtered, and the collect-
ed solids were washed with pentane (3ꢅ3 mL) to afford the
title compound as a microcrystalline solid.
[8] a) D. V. Partyka, Chem. Rev. 2011, 111, 1529–1595;
b) D. V. Partyka, A. J. Esswein, M. Zeller, A. D.
Hunter, T. G. Gray, Organometallics 2007, 26, 3279–
3282; c) D. V. Partyka, J. B. Updegraff III, M. Zeller,
A. D. Hunter, T. G. Gray, Organometallics 2009, 28,
1666.
[9] a) L. Gao, M. A. Peay, D. V. Partyka, J. B. Updegraff,
T. S. Teets, A. J. Esswein, M. Zeller, A. D. Hunter,
T. G. Gray, Organometallics 2009, 28, 5669–5681;
b) D. V. Partyka, T. S. Teets, M. Zeller, J. B. Updegraff,
A. D. Hunter, T. G. Gray, Chem. Eur. J. 2012, 18, 2100–
2112.
[10] As far as we are aware, only 2 examples using IPr and
SIPr as ligands has been reported in the litterature
using Grayꢂs conditions for the synthesis of arylgold
compounds (see ref.[8a]).
Acknowledgements
We gratefully acknowledge the EPSRC and ERC (Advanced
Researcher Award to SPN) for funding. Umicore AG is
thanked for its generous gifts of materials. SPN is a Royal
Society Wolfson Research Merit Award holder.
[11] CCDC 863704 (5) and CCDC 863705 (17) contain the
supplementary crystallographic data for this contribu-
tion. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[12] a) P. de Fremont, N. M. Scott, E. D. Stevens, S. P.
Nolan, Organometallics 2005, 24, 2411–2418; b) S. P.
Nolan, Acc. Chem. Res. 2011, 44, 91–100.
References
[1] a) A. Cormam, H. Garcia, Chem. Soc. Rev. 2008, 37,
2096–2126; b) C. Della Pina, E. Falletta, L. Prati, M.
Rossi, Chem. Soc. Rev. 2008, 37, 2077–2095; c) A. S. K.
Hashmi, Chem. Rev. 2007, 107, 3180–3211.
[2] a) P. Dube, F. D. Toste, J. Am. Chem. Soc. 2006, 128,
12062–12063; b) L. Zhang, J. Am. Chem. Soc. 2005,
127, 16804–16805; c) H. Schmidbaur, in: Organogold
compounds, (Ed.: A. Slawisch), Springer, Berlin, 1980;
d) H. Schmidbaur, A. Grohmann, M. E. Olmos, in: Or-
ganogold Chemistry, (Ed.: H. Schmidbaur), Wiley, Chi-
chester, 1999; e) S. A. Blum, J. J. Hirner, Y. Shi, Acc.
Chem. Res. 2011, 44, 603–613; f) K. E. Roth, S. A.
Blum, Organometallics 2010, 29, 1712–1716; g) K. E.
Roth, S. A. Blum, Organometallics 2011, 30, 4811–4813.
[3] a) M. A. Bennett, S. K. Bhargava, K. D. Griffiths, G. B.
Robertson, Angew. Chem.1987, 99, 262–264; Angew.
[13] a) A. O. Aliprantis, J. W. Canary, J. Am. Chem. Soc.
1994, 116, 6985–6986; b) T. Morita, N. Miyaura, A.
Suzuki, Synlett 1994, 149–151; c) R. Kakino, I. Shimizu,
A. Yamamoto, Bull. Chem. Soc. Jpn. 2001, 74, 371–376;
d) A. A. C. Braga, N. H. Morgon, G. Ujaque, F. Mase-
ras, J. Am. Chem. Soc. 2005, 127, 9298–9307;
e) A. A. C. Braga, N. H. Morgon, G. Ujaque, A.
Lledꢆs, F. Maseras, J. Organomet. Chem. 2006, 691,
4459–4466.
[14] J. F. Hartwig, B. P. Carrow, J. Am. Chem. Soc. 2011,
133, 2116–2119.
[15] C. Amatore, A. Jutand, G. Le Duc, Chem. Eur. J. 2011,
17, 2492–2503.
[16] F. D. Toste, E. Tkatchouk, N. P. Mankad, D. Benitez,
W. A. Goddard, J. Am. Chem. Soc. 2011, 133, 14293–
14300.
[17] S. Gaillard, A. M. Z. Slawin, S. P. Nolan, Chem.
Commun. 2010, 46, 2742–2744.
[18] Computations were performed at the PBE0-D3/SDD/
6–311+G** level, for computational details see the
Supporting Information.
ˇ
´
Chem. Int. Ed. Eng. 1987, 26, 260–261; b) M. Pazicky,
A. Loos, M. J. O. Ferreira, D. Serra, N. Vinokurov, F.
¨
Rominger, C. Jakel, M. Limbach, A. S. K. Hashmi, Or-
ganometallics 2010, 29, 4448–4458; c) R. Usꢆn, A.
Laguna, M. Laguna, I. Colera, E. De Jesffls, J. Organo-
met. Chem. 1984, 263, 121–129; d) J. Vicente, A. Arcas,
P. G. Jones, J. Lautner, J. Chem. Soc. Dalton Trans.
1990, 451–456.
[4] A. Sladek, S. Hofreiter, M. Paul, H. Schmidbaur, J. Or-
ganomet. Chem. 1995, 501, 47–51.
[19] Arguably, the putative s-bond metathesis on path A
will have a higher barrier than the DH° ꢀ7 kcalmolÀ1
required for chloride substitution; thus, intrinsically
(i.e., without counterions), the system in Scheme 3
would clearly prefer path B.
[5] J. M. Forward, J. P. Fackler, R. J. Staples, Organometal-
lics 1995, 14, 4194–4198.
[6] D. V. Partyka, M. Zeller, A. D. Hunter, T. G. Gray,
Angew. Chem. 2006, 118, 8368–8371; Angew. Chem. Int.
Ed. 2006, 45, 8188–8191.
[20] Initial experiments with KO-t-Bu instead of KOH
under optimum conditions in Table 1 leads to product
formation in 30 min. The role of alternative alkoxide
bases is presently being further explored.
[7] a) A. S. K. Hashmi, T. D. Ramamurthi, F. Rominger, J.
Organomet. Chem. 2009, 694, 592–597; b) D. Y. Melgar-
ejo, G. M. Chiarella, J. P. Fackler Jr, Acta Crystallogr.
Sect. C 2009, 65, 299.
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8 The Role of Metal Hydroxide Complexes in Late Transition
Metal-Mediated Transmetalation Reaction: The Case of
Gold
Adv. Synth. Catal. 2012, 354, 1 – 8
Stꢀphanie Dupuy, Luke Crawford, Michael Bꢁhl,
Alexandra M. Z. Slawin, Steven P. Nolan*
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ꢃ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 0000, 000, 0 – 0
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